Small angle x-ray scattering experiments were carried out on the all-ferrous state of the nitrogenase iron protein from Azotobacter vinelandii. The purpose of the experiments was to investigate the influence of nucleotide binding (MgATP and MgADP) on the protein structure in solution. Previous SAXS experimentson the wild-type protein showed an ~2.0 E decrease in the radius of gyration upon binding MgATP but not MgADP. Other experiments including EPR, CD, electrochemistry and chelation experiments have demonstrated that the [4Fe-4S] cluster undergoes a conformational change upon binding nucleotide. Just recently, the unprecedented all-ferrous form of the iron protein was produced with the addition of titanium citrate as the reductant. XAS studies showed that the all-ferrous [4Fe-4S] cluster had a structure very different from that of typical [4Fe-4S] clusters; however, experiments demonstrated that the all-ferrous form of the protein was indeed able to bind nulcleotide and transfer electrons for substrate reduction. We were interested in investigating whether or not the all-ferrous form of the protein unwent similar structural changes upon nucleotide binding.